At present, propane or lpg is used for drying grain such as wheat, and other agricultural products such as cotton. An advantage of using propane or similar liquid or gaseous fuel which burns clean is that the products of combustion are directly used for grain drying by passing these combustion products through the grain or other comodity. A relatively simple burner system can be used with such fuels, and the control of heat output is easy to regulate simply by regulating the flow of fuel to the burners.
However, in recent years, the price of such fuels has increased significantly, with the result that the cost of grain drying or cotton drying has increased significantly, and the cost is particularly high in regions of the country somewhat removed from wells which produce such gas. Further, the products of combustion of such clean burning fuels form water as a principal exhaust component, and correspondingly, the combustion products have a relatively high moisture content. As a result, some of the heat generated by burning the fuel is lost because this heat is required to remove the moisture added by the products of combustion.
Large quantities of hot air are also required for other uses such as factory heating, and industrial processes requiring heated air.
Correspondingly, there is a need for a heater or furnace for providing large quantities of hot air, particularly by burning a solid fuel such as coal, or lignite, or similar products, as well as very low grade solid fuels such as wood pellets, corn cobs, distressed corn, or sunflower hulls, and which can also be used to burn liquid or gaseous fuels should the price of such fuels be competitive, or desireable.